Precursors for making low dielectric constant materials with improved thermal stability

ABSTRACT

Fluorinated chemical precursors, methods of manufacture, polymer thin films with low dielectric constants, and integrated circuits comprising primarily of sp 2 C—F and some hyperconjugated sp 3 C—F bonds are disclosed in this invention. Precursors are disclosed for creating fluorinated silanes and siloxanes, and fluorinated hydrocarbon polymers. Thermal transport polymerization (TP), chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), high density PECVD (HDPCVD), photon assisted CVD (PACVD), and plasma-photon assisted (PPE) CVD and PPETP of these chemicals provides thin films with low dielectric constants and high thermal stabilities for use in the manufacture of integrated circuits.

CROSS REFERENCES

This application is a divisional of Ser. No. 09/440,297 filed Nov. 15,1999, now U.S. Pat. No. 6,248,407, which is a divisional of Ser. No.08/957,481, filed Oct. 24, 1997, now U.S. Pat. No. 6,020,458, issuedFeb. 1, 2000.

Lee et al., Chemicals and Processes for Making FluorinatedPoly(Para-Xylylenes). Attorney Docket No.: QTII 8021 SRM/DBB.

Lee et al., New Deposition Systems and Processes for TransportPolymerization and Chemical Vapor Deposition. Attorney Docket No.: QTII8022 SRM/DBB.

Lee et al., Low Dielectric Constant Materials with Improved Thermal andMechanical Properties. Attorney Docket No.: QTII 8023 SRM/DBB.

Lee et al., Low Dielectric Constant Materials Prepared from Photon orPlasma Assisted Chemical Vapor Deposition and Transport Polymerizationof Selected Compounds. Attorney Docket No.: QTII 8024 SRM/DBB.

All of the above co-pending applications are herein incorporated fullyby reference.

FIELD OF THE INVENTION

This invention relates to the precursors for manufacturing dielectricmaterials with low dielectric constants for use in the manufacture ofsemiconductor integrated circuits. The invention also relates to thepolymers made from these precursors, the processes used to makepolymers, and the integrated circuits made from these polymers.

BACKGROUND OF THE INVENTION

As integrated circuits (ICs) have become progressively moremicrominiaturized to provide higher computing speeds, the low dielectricconstant polymers used in the manufacturing of the ICs have proven to beinadequate in several ways. Specifically, they have not had sufficientthermal stability, generate toxic byproducts, are inefficient tomanufacture, and the dielectric constants are too high.

During the past few years, several types of precursors have been used tomanufacture polymers with low dielectric constants for use inmanufacture of integrated circuits (IC). Transport Polymerization (TP)and Chemical Vapor Deposition (CVD) methods have been used to depositlow dielectric materials. The starting materials, precursors and endproducts fall into three groups, based on their chemical compositions.The following examples of these types of precursors and products aretaken from Proceedings of the Third International Dielectrics for UltraLarge Scale Integration Multilevel Interconnect Conference (DUMIC), Feb.10-11 (1997).

I. Modification of SiO₂ by Carbon (C) and Fluorine (F)

The first method described is the modification of SiO₂ by adding carbonand/or fluorine atoms. McClatchie et al., Proc. 3d Int. DUMICConference, 34-40 (1997) used methyl silane (CH₃—SiH₃) as a carbonsource, and when reacted with SiH₄ and the oxidant H₂O₂ and depositedusing a thermal CVD process, the dielectric constant (K) of theresulting polymer was 3.0. However, this K is too high to be suitablefor the efficient miniaturization of integrated circuits.

Sugahara et al., Proc. 3d Int. DUMIC Conference, 19-25 (1997) depositedthe aromatic precursor, C₆H₅—Si—(0CH₃)₃ on SiO₂ using a plasma enhanced(PE) CVD process that produced a thin film with a dielectric constant Kof 3.1. The resulting polymer had only a fair thermal stability (0.9%weight loss at 450° C. in 30 minutes under nitrogen). However, the 30min heating period is shorter than the time needed to manufacturecomplex integrated circuits. Multiple deposition steps, annealing, andmetalizing steps significantly increase the time during which a wafer isexposed to high temperatures. Thus, this dielectric material isunsuitable for manufacture of multilevel integrated circuits.

Shimogaki et al., Proc. 3Int. DUMIC Conference, 189-196 (1997) modifiedSiO₂ using CF₄ and SiH₄ with NO₂ as oxidant in a PECVD process. Theprocess resulted in a polymer with a dielectric constant of 2.6, whichis lower than that of SiO₂.

However, one would expect low thermal stability due to low bondingenergy of sp³C—F and sp³C—Si bonds (BE=110 and 72 kcal/mol.,respectively) in the film. The low thermal stability would result infilms which could not withstand the long periods at high temperaturesnecessary for integrated circuit manufacture.

II. Amorphous-Carbon (αC)- and Fluorinated Amorphous Carbon(F-αC)-Containing Low Dielectric Materials

The second approach described involves the manufacture of α-carbon andα-fluorinated carbon films. Robles et al., Proc. 3d Int. DUMICConference, 26-33 (1997) used various combinations of carbon sourcesincluding methane, octafluorocyclobutane and acetylene with fluorinesources including C₂F₆ and nitrogen trifluoride (NF₃) to deposit thinfilms using a high density plasma (HDP) CVD process.

The fluorinated amorphous carbon products had dielectric constants aslow as 2.2 but had very poor thermal stability. These materials shrankas much as 45% after annealing at 350° C. for 30 minutes in nitrogen.

One theory which could account for the low thermal stability of thefluorinated amorphous carbon products is the presence of large numbersof sp³C—F and sp³C—sp³C bonds in the polymers. These bonds have abonding energy of 92 kcal/mol. Thus, the films can not withstand thelong periods of high temperatures necessary for IC manufacture.

III. Fluorinated Polymers

The third approach described uses fluorinated polymers. Kudo et al.,Proc. 3d Int. DUMIC Conference, 85-92 (1997) disclosed polymers madefrom C₄F₈ and C₂H₂ with a dielectric constant of 2.4. The polymers had aTg of 450° C. (Kudo et al., Advanced Metalization and InterconnectSystems for ULSI Applications; Japan Session, 71-75 (1996)).

However, despite its low leakage current due to presence of sp³C—Fbonds, a low thermal stability can be expected due to presence of sp³C—Fand sp³C—sp³C bonds in the films. Thus, like the F-αC-containingpolymers discussed above, these fluorinated polymers are unable towithstand the prolonged high temperatures necessary for IC manufacture.

LaBelle et al, Proc. 3d Int. DUMIC Conference, 98-105 (1997) madeCF₃—CF(O)—CF₂ polymers using a pulsed plasma CVD process, which resultedin a polymer film with a dielectric constant of 1.95. However, in spiteof the low K, these polymer films would be expected to have low thermalstability due to presence of sp³C—sp³C and sp³C—O bonds in these filmswhich have bonding energies of 85 kcal/mol.

Therefore, none of the previously described low dielectric materialshave suitably low K and high thermal stability necessary for ICmanufacturing.

Wary et al, (Semiconductor International, June 1996, 211-216) used theprecursor, (α, α, α¹, α¹) tetrafluoro-di-p-xylylene) or{—CF₂—C₆H₄—CF₂—}₂ Parylene AF-4™, which contains a non-fluorinatedaromatic moiety, and a thermal CVD process to manufacture Parylene AF-4™which has the structural formula: {—CF₂—C₆H₄—CF₂—})_(n). Films made fromParylene AF-4™ have a dielectric constant of 2.28 and have increasedthermal stability compared to the above-mentioned dielectric materials.Under nitrogen atmosphere, a polymer made of Parylene AF-4™ lost only0.8% of its weight over 3 hours at 450° C.

However, in spite of the advantages of conventionalpoly(para-xylylenes), there are disadvantages of the known methods oftheir manufacture. First, the manufacture of their precursors isinefficient because the chemical reactions have low yields, and theprocess is expensive and produces toxic byproducts. Further, it isdifficult to eliminate redimerization of the reactive intermediates.When deposited along with polymers, these dimers decrease the thermalstability and mechanical strength of the film.

Thus, the prior art contains no examples of dielectric materialprecursors for semiconductor manufacture which have desired propertiesof low dielectric constant, high thermal stability, and low cost.

SUMMARY OF THE INVENTION

The present invention is directed to overcoming the disadvantages of theprior art.

Accordingly, one object of the invention is to provide precursormaterials which can be used to manufacture products including polymerswith low dielectric constants for IC manufacture.

Another object of the invention is to provide precursors which can bemanufactured into products which have high thermal stability.

Yet another object of the invention is to provide precursors which canbe polymerized as thin layers on a substrate.

An additional object of the invention is to provide precursor materialswhich are inexpensive.

A further object is to provide materials which can be made into productswith high efficiency.

An additional object of the invention is to provide precursors which canbe made into dielectric materials which can be easily and accuratelyshaped after manufacture.

The invention includes novel precursors containing a fluorinated silane,a fluorinated siloxane or a fluorocarbon each containing a fluorinatedaromatic moiety. The precursors are suitable for making polymers withlow dielectric constants and high thermal stability. The polymers can beused for making integrated circuits.

Additionally, the invention includes methods for making polymers forintegrated circuit manufacture using novel fluorinated silanes,fluorinated siloxanes, or fluorocarbons, each containing a fluorinatedaromatic moiety.

Furthermore, the invention includes integrated circuits comprising lowdielectric constant polymers made using fluorinated silanes, fluorinatedsiloxanes, or fluorocarbons, each containing a fluorinated aromaticmoiety.

Accordingly, one aspect of the invention comprises precursors for usingin manufacturing polymers with low dielectric constants which are usefulin the manufacture of integrated circuits (ICs).

Another aspect of the invention comprises precursors for use inmanufacturing polymers with high thermal stability which are useful inthe manufacture of ICs.

Another aspect of the invention comprises methods for reacting theprecursors and depositing them as thin films on substrates for ICmanufacture.

Yet another aspect of the invention comprises the deposited thin filmmade using the novel precursors and methods for their reaction anddeposition.

Another aspect of the invention is the integrated circuits comprised ofthin films derived through the reaction and deposition of the novelprecursors.

Other objects, aspects and advantages of the invention can beascertained from the review of the additional detailed disclosure, theexamples, the figures and the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Embodiment of an apparatus of this invention used forthermolytic transport polymerization of fluorinated silanes, fluorinatedsiloxanes, and fluorocarbons.

FIG. 2. Embodiment of an apparatus of this invention used for radiofrequency plasma enhanced transport polymerization of fluorinatedsilanes, fluorinated siloxanes, and fluorocarbons.

FIG. 3. Embodiment of an apparatus of this invention used for highdensity plasma enhanced chemical vapor deposition of fluorinatedsilanes, fluorinated siloxanes, and fluorocarbons.

FIG. 4. Embodiment of an apparatus of this invention used for photonassisted transport polymerization of fluorinated silanes, fluorinatedsiloxanes, and fluorocarbons.

FIG. 5. Embodiment of a universal deposition system of this inventionfor deposition of fluorinated silanes, fluorinated siloxanes, andfluorocarbons.

FIG. 6. Schematic cross-section view of a thin film of this inventionmade of polymers derived from fluorinated silanes, fluorinatedsiloxanes, and fluorocarbons.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

I. Precursors for Making Fluorinated Materials With Low DielectricConstant

This invention discloses novel precursors for making three categories offluorine-containing low dielectric materials. These precursors includefluorinated silanes, fluorinated siloxanes, and fluorocarbons. Thedielectric materials are useful in the manufacture of semiconductors forintegrated circuits and other electronic devices. Manufacture of smallerand faster integrated circuits requires intermetal dielectric (IMD) andinterlevel dielectric (ILD) materials which minimize the communicationof electrical signals between adjacent conductive lines, referred to asthe interconnects. Low dielectric materials are useful to minimize this“cross-talk” within and between layers of integrated circuits.

The polymers prepared from the precursors of the present invention arerigid and contain a high degree of substitution of hydrogen atoms byfluorine atoms. In these polymers, the fluorine in the aromatic ringprovides the low dielectric constant (K) below about 0.3 and molecularrigidity. This rigidity is reflected by high glass transitiontemperature (Tg) temperature of decomposition above about 300° C., highelastic modulus (E) and high shear modulus (G). The elastic modulus isabove about 2, and preferably is about 3.

One theory for the thermal stability of the poly(para-xylylenes) is thatthe higher bonding energies of the sp²C═sp²C, sp²C—H and sp²C—sp³C bondsof 145, 111 and 102 kcal/mol. respectively. In addition, the sp³C—Fbonds may also be involved in hyperconjugation with sp²C═sp²C doublebonds of the adjacent phenylene groups in Parylene AF-₄™. Thishyperconjugation renders a higher bond energy for the sp³C—F bonds thanthat found in non-hyperconjugated sp³C- bonds. (See A. Streitwiesser etal., Introduction to Organic Chemistry, Appendix II, University ofCalifornia Press, Berkeley, Calif. (1992)) (Table 1).

TABLE 1 Energies of Carbon Bonds In Dielectric Polymers Bond Type:sp³C—Si sp²C—Si sp³C—sp³C sp²C—H sp²C—F sp³C—H Bond Energy 72 92 92 111126 86 (kcal/mol) Bond Type: sp³C—O sp²C—sp³C sp²═sp²C sp³C—F sp³Si—FBond Energy 85 102 145 110 135 (kcal/mol)

Thus, carbon atoms bonded to other atoms by with sp²C═sp²C, sp²C—F andhyperconjugated sp³C—F bonds confer advantages to polymers containingthem, whereas other types of bonds (such as sp³C—H and sp³C—C bonds) donot confer these advantages. The sp²C=sp²C and other sp²C bonds increasethe mechanical strength and increase Td of the polymer. The presence offluorine atoms in the aromatic moieties of the polymers of thisinvention decreases the dielectric constant, and the sp²C—F andhyperconjugated sp³C—F bonds confer greater thermal stability to apolymer containing them. In contrast, polymers which do not containthese types of bonds have lower thermal stability and higher dielectricconstant. As one can see from Table 1, although precursors containingsp²C=sp²C bonds have high thermal stability (bond energy=145 kcal/mol),it is not desirable to use any non-fluorinated compound that consists ofthese chemical bonds as starting material. Using these non-fluorinatedcompounds as starting material for PECVD will result in high thermalstability, however, the resulting polymer will also have an highdielectric constant (K>2.5). Therefore, materials with low dielectricconstants, high elastic and shear moduli (E and G, respectively) andhigh thermal stability Tg and Td) can be obtained only if thefluorinated compounds of this invention are used.

The above conclusions are derived from calculations using an extended“Quasi-Lattice theory” (C. Lee, JMS Rev. Macromol. Chem. Phys.,C29(4):431-560 (1989), incorporated herein fully by reference, and a“topological approach” employed by J. Bicerano, Prediction of PolymerProperties, Second Edition, Marcel Dekker, Inc., New York (1996),incorporated herein fully by reference, indicated that low dielectricconstant materials with high thermal stability and high rigidity can beachieved with precursors containing sp²C—F and sp²C bonds.

Although the above calculations using cohesive energy may account forthe mechanical and electrical properties of dielectric materials of thepresent invention, other theories may also explain the observations.Accordingly, the instant invention is not limited to any particulartheory which may explain the desired properties of the herein discloseddielectric precursors.

Therefore, the precursors of this invention contain both single andconjugated double bonds. Additionally, hyperconjugation of sp³C—F withsp²C bonds results in increased bond strength of the sp³C—F compared toother sp³ C—F bonds (such as in polytetrafluoroethylene) which are nothyperconjugated.

However, although precursors which contain double bonded carbon atomswithout fluorine (sp²C═sp²C) have desirable Td, Tg, E, and G, thedielectric constant K is too high to be useful in the newer, smallerintegrated circuits. Thus, the invention comprises incorporatingfluorine atoms bonded to the double bonded carbon atoms in the precursormolecules (sp²C—F) into dielectric materials.

The precursors comprise compounds containing sp²C—F bonds and functionalgroups which can be cleaved or oxidized using a transport polymerization(TP) or chemical vapor deposition (CVD) process to yield reactiveintermediates which spontaneously polymerize on the wafer substrate.Both linearly conjugated polymers and aromatic moieties can be used, butpreferred moieties are aromatic. Also preferred are multiple-ringaromatic moieties, and the most preferred are single-ring aromaticmoieties such as phenyl rings (e.g., —C₆H₄—, —C₆H₅).

A single fluorine atom incorporated into an aromatic moiety decreasesthe dielectric constant of that moiety, and further Increasing thenumber of fluorine atoms in the aromatic moiety further decreases K.Thus, the general formula for mono-fractional aromatic precursors of theinvention is: —C₆H_(5-n)F_(n), wherein n is an integer selected from thegroup of 1, 2, 3, 4 or 5. Similarly, the general formula fordi-functional aromatic precursors is: —C₆H_(4-n)F_(n)—, wherein n is aninteger selected from the group of 1, 2, 3 or 4. The most preferredembodiments are aromatic moieties which have maximal substitution ofsp²C—H hydrogen atoms by sp²C—F fluorine atoms. Thus, for a precursorcontaining only one functional group, the mono-fluorinated phenyl group—C₆H₄F works, but multi-fluorinated phenyl groups are preferred, and—C₆F₅ is most preferred. For a precursor containing two functionalgroups, the mono-fluorinated phenyl group —C₆H₃F— works, butmulti-fluorinated phenyl groups are preferred, and —C₆F₄— is mostpreferred.

A. Fluorocarbon-Modified SiO₂: Fluorinated Silanes and FluorinatedSiloxanes

The first category of precursors consists of precursors for makingfluorocarbons, fluorinated silanes and fluorinated siloxane. Theseprecursors are useful for modifying SiO₂ by incorporating Si—C bonds,Si—F bonds, and/or fluorinated aromatic bonds. Incorporation of thesetypes of bonded moieties into SiO₂ can lower the dielectric constant,but with only small decreases of the Td, Tg, E, and G of the polymersfrom which they are made.

Precursors of fluorinated silanes in this invention have the generalstructural formula: (C₆H_(5-n)F_(n))_(m)—SiH_(4-m), wherein n is 1, 2,3, 4 or 5 and n is an integer of 1, 2, 3 or 4. The preferred fluorinatedsilane of the present invention is C₆F₅—SiH₃.

Precursors of fluorinated siloxanes of this invention have the generalstructural formula: (C₆H_(5-n)F_(n))_(m)—Si(OCH₃)_(4-m), wherein n is 1,2, 3, 4 or 5, and m is 1, 2, or 3. The preferred fluorinated siloxane ofthe present invention is (C₆F₅)—Si(OCH₃)₃.

Precursors of fluorinated hydrocarbons have the general structuralformula: CH_(3-n)F_(n)—C₆H_(4-p)F_(p)—CH_(3-m)F_(m), wherein n and m are1, 2 or 3, and p is 1, 2, 3, or 4. Preferred fluorinated hydrocarbonprecursors are CF₃—C₆F₄—CF₃ and CHF₂—C₆F₄—CHF₂.

There are many isomers with these above general formulas, and all areconsidered part of the present invention.

TABLE 2 Precursors and Methods for Manufacturing Low Dielectric SiO₂Derivatives C & F-source Si Source Oxidant TP and CVD ProcessesC₆F₅—SiH₃ SiH₄ H₂O₂, NO₂ Thermal C₆F₅—Si(OCH₃)₃ — — Plasma EnhancedCF₃—C₆F₄—CF₃ SiH₄ — Plasma Enhanced

Table 2 shows the precursors, other reactants and TP and CVD processesused to manufacture fluorine-substituted aromatic SiO₂ derivatives ofthis invention. Although the fully fluorinated derivatives aredescribed, mono-, di-, tri-, and tetra-fluorinated aromatic moieties, asappropriate, can also be used.

B. Precursors for Making Fluorinated Amorphous Carbon- andPolymer-Containing Materials With Low Dielectric Constant

These precursors consist primarily of sp²C═sp²C, sp²C—F and/orhyperconjugated sp³C—F bonds. Unlike the precursors used for makingsilanes and siloxanes, no Si source is needed.

Precursors for fluorinated polymers ,with one aromatic ring and onesp²C—sp³C—F type bond have the general formula:(C₆H_(5-n)F_(n))—CH_(3-m)F_(m), where n is an integer of 1, 2, 3, 4, or5, and m is an integer of 1, 2, or 3. A preferred precursor of afluorinated polymer is C₆F₅—CF₃.

Precursors for fluorinated polymers with one aromatic ring and twosp²C—sp³C—F type bonds have the general formula:(CH_(3-n)F_(n))—(C₆H_(4-p)F_(p))—(CH_(3-m)F_(m)), wherein n and m areintegers selected from the group consisting of 1, 2 and 3, and p is aninteger selected from the group consisting of 1, 2, 3, and 4. Theprecursors of fluorinated polymers which are commercially availableinclude CF₃—C₆F₄—CF₃ and CHF₂—C₆F₄—CHF₂.

Precursors of polymers containing one fluorinated aromatic residue andan additional conjugated sp²C carbon bond have the general structuralformula: (C₆H_(5-n)F_(n))—CH_(1-m)F_(m)═CH_(2-p)F_(p), where n is aninteger of 1, 2, 3, 4, or 5, m is an integer of 0 or 1, and p is aninteger of 0, 1, or 2. The preferred precursor of this group isC₆F₅—CF═CF₂.

There are many isomers with these above general formulas, and all areconsidered part of the present invention.

TABLE 3 Precursors for Making Low Dielectric Hydrocarbon Polymers C &F-sources Primary α-C Source TP or CVD Process C₆F₅—CF₃ CH₄ High DensityPlasma C₆F₅—CF═CF₂ CH₄ High Density Plasma HCF₂—C₆F₄—CF₂H Thermal orPhoton Assisted CF₃—C₆F₄—CF₃ Photon Assisted

II. Deposition of Low Dielectric Materials

The invention comprises new methods and precursors for depositing lowdielectric materials. These new methods and precursors have advantagesover conventional methods.

During conventional manufacture of semiconductors using spin-on glass(SOG) methods, defects in the dielectric layers can form, especially inlocations where there is a channel between metal lines. Such defects inthe dielectric layers result in the formation of cracks or “voids” inthe dielectric material. These voids and cracks result in trappingmoisture, etching gas, or photoresist contaminants and ultimately leadto the degradation and loss of device reliability. Therefore, thepresent invention provides precursors which can be deposited usingchemical vapor deposition (CVD) and transport polymerization (TP) toavoid the problem.

In CVD, a precursor is placed directly on the substrate which will havethe thin film of low dielectric material applied. In his “hot chuck”method, the wafer and precursor are exposed to an energy source such asheat, plasma, or electromagnetic radiation to “dissociate” or “crack”the precursor molecule directly on the wafer to form the reactiveintermediate. The reactive intermediate molecules then polymerize witheach other to form the thin film.

In TP, the cracking step is performed an a chamber other than where thedeposition step is performed. This “cold-chuck” method confers severaladvantages. First, the cracking efficiency can be optimized by selectingappropriate conditions of plasma density, photon energy, or temperature.Second, the density of the intermediate molecules can be regulated tominimize the formation of unwanted side products, such as re-formedprecursors. Next, because the wafer is not exposed to the harshconditions of precursor dissociation, fragile structures containingaluminum or other thermally sensitive materials are less likely tobecome damaged. Deposition of polymer layers of a few nanometers (nm)to>7000 nm can be achieved, along with eliminating or greatly reducingthe number of voids. In principle, layers of polymer of moleculardimensions can be deposited. Thus, the invention provides the novelprecursors for the deposition of void-free dielectric films. The type offunctional group used determines the optimal type of TP or CVD processshould be used. These will be discussed below.

A. General Processes for the Manufacture of Fluorinated AromaticDerivatives of Silanes and Siloxanes Using Thermal TransportPolymerization and Chemical Vapor Deposition

For preparations of the low K dielectrics of this embodiment accordingto the Table 2, the concentration of the fluorinated aromatic silane isin the range of from about 5% to 100%, and is preferably 20%. Thefluorinated aromatic siloxane is used in the range of from about 5% toabout 100%, and is preferably 20%. In a plasma enhanced chemical vapordeposition (PECVD) and photon-assisted transport polymerization (TP)processes, no oxidants are required, but in a thermal TP or thermal CVDprocess an oxidant such as H₂O₂ or NO₂ is added to oxidize the Si atomsof SiH₄ or other silane. Other suitable oxidants are oxygen containingorganic or in organic compounds, such as oxalic acid. When H₂O₂ is used,its concentration should be in the range of about 10% to about 50%, andis preferably about 30%.

Thermal TP is carried out in a chamber 100 shown in FIG. 1. Theprecursors are contained within a precursor tank 104, flow through apipe 108 into a mass flow controller 112 from which they arecontrollably released through another pipe 116 into the chamber 120within which is a container 124 with a cracking device that may comprisea catalyst 128. The precursors are heated by a conventional resistiveheater 132 to generate the reactive intermediate radicals. Rates ofprecursor flow range from 0.2 SCCM to 100 SCCM, preferably between 2 and5 SCCM, and most preferably at 3 SCCM. Temperatures of reactions withoutcatalysts should range from about 700° C. to about 800° C., preferablyare in the range of from about 700° C. to about 750° C., and mostpreferably at about 750° C. For reactions in the presence of catalysts,temperatures can be as low as about 350° C. The pressure in the chamber120 needed for the cracking reaction should be in the range of about 1milliTorr to about 500 Torr, and is preferably about 10 milliTorr. Aftercracking, the intermediates flow to a diffusion plate 136 where the bulkflow is diverted away from the wafer 140. The diffusion plate 136 can bepositioned as desired within the chamber, to optimize the pattern offlow of intermediates to the wafer. The intermediates then diffuse tothe wafer 140, which is held on a cold chuck 144 which is maintained ata temperature lower than the cracking device by a chiller 148.Temperatures are maintained by any conventional cooling method includingliquid nitrogen or reverse Peltier methods. Temperatures of the chuckshould be in the range of about −120° C. to about 300° C. are useful,preferred temperatures are in the range of about −40° C. to about 100°C., and the most preferred temperature is about −20° C. The chamber 120is connected via a pipe 152, to a cold trap 156, and another pipe 160connects the trap to a pump 156 to maintain low pressure in the chamber120. The cold trap 156 protects the pump 160 from deposition ofprecursors and intermediates in the chamber 120.

1. Use of Catalysts in Thermal TP and Thermal CVD

Thermal TP and CVD processes requiring catalysts to dissociate precursormolecules into reactive intermediates can use any conventional catalyst.An ideal catalyst useful for this invention should provide highreactivity, high selectivity, long process life cycle, high recyclecapability, and less severe pressure and temperature requirements. Itshould be inexpensive, safe for human handling, and should beenvironmentally friendly. The catalyst should crack or cleave the Si—Hand crack or oxidize the C—H bonds. Further, the catalyst should not addany metal or metal compound, or reactive ion such as F⁻ into thedielectric film during deposition. Serious reliability problems occurwhen a metal contaminant resides within the dielectric materials. Otherserious problems occur when a highly reactive ion such as F⁻ isintroduced into the film. The ion can break interatomic bonds within thehydrocarbon moieties of the dielectric material, resulting in loweredmechanical strength.

Catalysts that are useful for this invention include dehydrogenationcatalysts, reforming catalysts, and oxidative dehydration catalysts.

a. Dehydrogenation Catalysts

The temperatures and times needed to complete pyrolysis can be reducedby employing a catalyst in the chamber. An ideal catalyst useful forthis invention should provide high reactivity, high selectivity, longprocess life cycle, high recycle capability, and less severe pressureand temperature requirements. It should be inexpensive, safe for humanhandling, and should be environmentally friendly. The ideal catalystshould crack or cleave the Si—H and C—H bonds without cracking orcleaving the C—F bonds. Further, the catalyst should not add any metalor metal compound into the dielectric film during deposition. Seriousreliability problems occur when a metal contaminant resides within thedielectric materials.

To assist the cracking of the SiH and C—H bonds, any commonly useddehydrogenation catalyst is suitable. These catalysts are also called“protolytic cracking catalysts”, or “oxidative dehydrogenationcatalysts”, in petroleum processing. Additionally, most“dehydrocyclization catalysts” and some of the “aromatization catalysts”for hydrocarbon processing are also useful for this invention, becausearomatization normally involves dehydrogenation.

Potassium ferrite (KFeO₂) on iron oxide is an example of a suitablecatalyst which is commercially available. The ferrite commonly comprisesa promoter that may contain a salt of oxide of a Group (IIA) metal, suchas Mg, Ca, or Sr, and a Group VB or VIB metal, such as V, Nb, Cr, Mo. orW. [See J. I. Krochiwitz ed., Encyclopedia of Chemical Technology, 4thedition, Catalysis and Catalysts, Vol. 5: 320 (1991), incorporatedherein fully by reference.] These catalysts can be useful attemperatures up to about 600° C. Variations of these catalysts areBASF's Lu-144F™ and Shell 105™ catalysts, and catalysts for thedehydrogenation of ethylbenzene. These include those produced byMonsanto-Combustion Engineering-Lumis, Union Carbide-Cosden-Badger, andSociete-Chimique des Charbonnages. [See J. J. McKetta, Ed., Encyclopediaof Chemical Processing and Designs: Dehydrogenation, Vol. 14:276, MarcelDekker Inc. (1992), incorporated herein fully by reference.]

Other industrial catalysts include Cu and Zn oxides on alumina and Cu,Ag or Cu—Ag alloy in the form of gauge or as metal deposited on a lowsurface area support such as kaolin, clay and active carbon. Othersupports or carriers can include asbestos, pumice, kiesselguhr, bauxite,CuO, Cr₂O, MgCO₃, ZrO₂, and Zeolites. These catalysts are active byvirtue of an oxide layer on the metals, and are used for hydrogengeneration from methanol. Catalysts consist of copper chromite, bismuthmolybdate, iron molybdate, or tin phosphate on similar supports are alsouseful. [See J. I. Krochiwitz ed., Encyclopedia of Chemical Technology,4th edition, Catalysis and Catalysts, Vol. 5: 320 (1991), incorporatedherein fully by reference; J. J. McKetta, Ed., Encyclopedia of ChemicalProcessing and Designs: Dehydrogenation, Vol. 14:276, Marcel Dekker Inc.(1992), incorporated herein fully by reference.]

b. Reforming Catalysts

In addition to dehydrogenation catalysts, reforming catalysts used inpetroleum reforming processes can also be used. A first group of theseinclude transition metal oxides, such as V₂O₅, MoO₃, WO₃ and Cr₂O₃ inbulk form or preferred on a non-acid support such as silica, neutralalumina or active carbon. [See Meriaudeau and Naccache, Cat. Rev.-Eng.Sci. 39(1&2):5-48 (1997), incorporated herein fully by reference.Typically useful catalysts include Shell 205™, which consists of 62.5%Fe₂O₃, 2.2% Cr₂O₃, and 35.3% K₂CO₃, and Dow Type B™ catalyst, whichconsists of calcium and nickel phosphates promoted with a small amountof chromium oxide.

Another group of reforming catalysts useful for dehydrogenation includenoble metals on acid supports. The most commonly used catalysts are Pt(0.3 to 0.7%) and Pt/Re on a chlorided (acidified) alumina (e.g., γ- orη-Al₂O₃). The bimetallic Pt/Re-alumina is preferred for its longer lifetime. In addition, Pt, Ga or An modified H-ZSM-5™, or Pt on medium-porezeolite support such as In-ZSM-5™ is also very effective.

Other, multimetallic reforming catalysts include Pt/Re catalysts of theabove including lesser amounts of Ir, Ga, Ge, Sn or Pb supported bychlorided alumina. The catalysts typically have surface areas rangingfrom 170 m²/g to 300 m²/g and pore volumes ranging from 0.45 cm³/g to0.65 cm³/g. [See J. I. Krochiwitz ed., Encyclopedia of ChemicalTechnology, 4th edition, Catalysis and Catalysts, Vol. 5: 320 (1991),incorporated herein fully by reference.] Additionally useful catalystscan also be found in the OJG International refining catalystcompilation-1987 (J. J. McKetta ed., Encyclopedia of Chemical Processingand Designs: Petroleum Processing, Catalyst Usage, Vol 35:87-89 MarcelDekker (1992), incorporated herein fully by reference.] These catalystscomprise active agents such as Pt/ReCl, Ni, PtCl and other rare earthmetals on alumina and zeolites.

Other useful catalysts in this invention include (1) noble metals ormetal sulfide on active carbon, (2) Ga₁₃, Cr₁₂, GaAl₁₂ & Al₁₃ on PILCs,(3) M—Al₂O₃ with M=lanthanides, (4) Al₂O₃ kneaded with M, where M is Bi& Sb compounded with periodic table Group VIB & VIIB metals, (5)M-modified H-ZSM-5 and H-ZSM-11 where M is Zn, Ga, Pt—Ga, Pt—Na, Mo, Cr,K, Ca, Mg, Al, and Group VIII metals, (6) M-modified MFI(H-GalloSilicates) where M is Si/Ga, Na/Ga, Al, (7) rare earth metalexchanged Y-zeolites or ultra stable Y-zeolites, (8) Ti oxide pairedwith Zr oxide, (9) M plated onto aluminum, where M is Ni, and Ni, Cr,and Al alloys.

Pure dehydrogenations are endothermic by 15 to 35 kcal/g-mol. and hencehave high heat requirements. The above catalysts are normally used attemperatures ranging from 300° C. to 600° C. depending on the residencetime of the chemicals in the reactor. The effective temperature for someof these catalysts can be lowered by adding free radical initiators suchas I, Br, H₂O, sulfur compounds or oxygen and their mixtures. However,special care should be taken to avoid reaction of desirable radicalswith free radicals generated from these initiators. This can be achievedby providing large mean free paths for these reactants in the reactor,reducing residence time and the adjustment of wafer temperatures toavoid condensation of low mass free radicals.

2. Loss Of Catalyst Function

With time, catalysts may lose reactivity due to changing their oxidativestate or coke formation. The life time of the catalysts can be increasedat high operating temperatures or high partial pressure of hydrogen. Ifcatalysts lose activity by coke accumulation, they can be regenerated bycareful oxidation followed by reduction with hydrogen before beingreturned to service. [See: J. J. McKetta ed., Encyclopedia of ChemicalProcessing and Designs: Catalysis and Catalysts Vol. 6:420; PetroleumProcessing, Catalyst Usage, Vol 35:89 Marcel Dekker, Inc. (1992),incorporated herein fully by reference.

After leaving the cracking device, the intermediates pass through adiffusion plate to disperse the intermediates evenly over the wafersurface. The intermediates deposit upon the wafer, which is held on achuck, which, in turn, is connected to a chiller to maintain atemperature of the chuck and wafer below the temperature of the chamberand the intermediates. The temperature of the cold chuck is maintainedin the range of about −30° C. to about +20° C., preferably at −20° C.Low pressure in the system is maintained by a vacuum pump withsufficient capacity to maintain the desired pressure within the CVDsystem. Condensation of precursors and intermediates on the pump isminimized by a trap placed between the deposition chamber and the vacuumpump.

EXAMPLE 1 Thermal CVD Of A Fluorinated Silane

The sp²C—F-modified SiO₂ thin films can be prepared from thermaloxidation of C₆F₅—SiH₃. An admixture of 40 mole % of SiH₄ and 60 mole %of C₆F₅—SiH₃ in an aqueous solution with 30% by weight of H₂O₂ aredispensed separately through two flash evaporators onto a cold waferinside a CVD system. The molar ratio of H₂O₂/(SiH₄+C₆F₅—SiH₃) is about3.5. The mixtures of H₂O₂, SiH₄, and C₆F₅—SiH₃ is chilled as a thin filmon the wafer. The wafer is then heated from −20° C. to 500° C. in vacuumat a heating rate of 10° C./min. The resulting thin film has adielectric constant of 2.7 and an initial decomposition temperature of480° C. when tested under nitrogen atmosphere.

B. General Methods for the Manufacture of Low Dielectric Thin FilmsUsing Plasma TP or CVD

Plasma enhanced TP is carried out generally using methods in the art.Takai et al., J. Appl. Phys. 17:399-406 (1984), incorporated hereinfully by reference. With low density plasma, the electron density in theplasma is in the range of about 10¹² to about 10¹³ electrons/cm³. Lowdensity plasma TP and CVD can be carried out at about 100 milliTorr toabout 100 Torr. High density plasma (HDP) is characterized by electrondensities in the range of about 10¹³ to about 10¹⁴ electrons/cm³. Highdensity plasma TP and CVD can be carried out at pressures of about 0.1milliTorr to about 100 milliTorr.

For preparation of the materials with low dielectric constants embodyingthis invention, reactants such as SiH₄, or more generally siloxane suchas Si(OCH₃)₄ are used. In a thermal CVD process, the presence of oxygenat high temperatures will induce oxidation, resulting in the formationof silicon dioxide (SiO₂) films having varying K based on varying therelative compositions of SiO₂ and sp²C—F bonded molecules.

1. Plasma Enhanced Transport Polymerization of Fluorinated Silanes andFluorinated Siloxanes

To make thin films, sp²C—F-containing starting materials such as(C₆H_(5-n)F_(n))_(m)—Si(0CH₃)_(4-m) wherein n is an integer of 1, 2, 3,4, or 5, and m is an integer of 1, 2, or 3,(C₆H_(5-n)F_(n))_(m)—SiH_(4-m) wherein n is an integer of 1, 2, 3, 4, or5, and m is an integer of 1, 2, 3, or 4, C₆F₅—CF₃, or admixtures ofthese starting materials are delivered into a plasma enhanced transportsystem 200 depicted in FIG. 2. Precursors are stored in a precursorholder 204. A carrier gas, typically helium, is passed through abubbling device to volatilize the precursor. The vaporized precursorsflow through a pipe 208 and to a mass flow controller 212. The mass flowcontroller (MFC) provides a precursor feed rate ranging from about 0.2to about 500 standard cubic centimeter per minute (SCCM). The precursorsflow from the MFC 212 through a pipe 216 and into a quartz tube 220under low pressures in the range of from about 0.1 milliTorr to 10 Torr,and preferably in the range from about 1 milliTorr to about 3 milliTorr.A carbon source such as CH₄ or C₂H₂ is provided via a second feeder (notshown) and a second MFC (not shown) with a feed rate ranging from 0 to500 SCCM. The preferred flow rates of precursor into the plasma tubeshould be in the range of from about 0.2 SCCM to about 10 SCCM, and ismost preferably in the range of about 0.5 SCCM to about 1 SCCM.

Pyrolization takes place within the quartz tube by action of aradiofrequency (RF) plasma generator 226. Effective plasma 230 can bemaintained by radio frequencies in a range of between about 1 kHz and2.5 GHz. A preferred range is between about 400 KHz and about 13.56 MHz.Ideally, the RF frequency is about 13.56 MHz. The RF power should be inthe range of about 30 Watts to 300 Watts, preferably about 100 Watts to250 Watts, and more preferably about 200 Watts.

The plasma 230 then proceeds into the deposition chamber 234 which isheated by a heater 238 to prevent deposition of precursor intermediateson the chamber walls. The pressure within the chamber 230 is maintainedat a pressure between about 0.1 milliTorr and about 10 Torr. The flow ofplasma is adjusted by a flow pattern adjuster 242, which can be movedwithin the chamber. Moving the flow pattern adjuster 242 in the verticaldirection adjusts the flow rate and distribution pattern of the plasmaas it enters the chamber. Moving the flow pattern adjuster in thehorizontal direction adjusts the distribution of plasma to differentparts of the wafer 250. A gas dispersion plate 246 evens the delivery ofthe intermediates to the wafer 250. The wafer 250 is cooled by the chuck254, which is cooled by liquid nitrogen, reverse Peltier effect, orother conventional cooling device 258, and is maintained at atemperature in the range of about −30° C. to about +20° C., and ispreferably about −10° C. The deposition chamber 224 is connected via apipe 262 to a cryogenic trap 266, which is connected via a pipe 270 to apump 276, which maintains the pressure within the chamber at the desiredlevel.

2. High Density Plasma Chemical Vapor Deposition

A high density plasma deposition process can also be used to dissociateprecursors. In contrast to the low density plasma process describedabove, in high density plasmas, the electron density is in the range offrom about 10¹³ to 10¹⁴ electrons/cm³. This process must be carried atlower pressures than conventional plasma processes. In this embodiment,a inductively coupled high density plasma apparatus 300 is shownschematically in FIG. 3. A precursor delivery system 304 volatilizes orvaporizes the precursor, which flows through a pipe 308 and an anode gasinjector 312 into the deposition chamber 316. The anode gas injector 312is attached to RF generators 320 which are matched by matchingcontrollers 324. The output of the RF generators 320 passes throughinductive coils 328 to produce an electrical field. The wafer 332 isheld by a cathode electrostatic chuck 336, which is connected to the RFgenerator 320. IR sources 340 provide additional heating of precursorsto decrease the needed plasma power and to inhibit condensation ofmaterials on the walls of the chambers. The plasma source power neededfor a wafer of 8 inch diameter is in the range of about 100 Watts to4000 Watts, and preferably about 2000 Watts. For wafer of other sizes,the power should be adjusted accordingly. Power should range from about1 Watt/cm² wafer surface area to about 15 Watts/cm², preferably fromabout 2 Watts/cm² to about 10 Watts/cm², and most preferably about 5Watts/cm². The chamber pressure is maintained in the range of 0.01milliTorr to 10 milliTorr, and preferably below 5 milliTorr. The wafertemperature is in the range from about 300° C. to 450° C., and ispreferably about 350° C.

Generally, thin films made using plasma methods contain lower carboncontent than films made using thermal methods. Films with decreasedcarbon content are made using greater plasma power. One theory toaccount for this is that increasing the plasma power increases thedissociation of the precursors by more completely cracking theprecursors. Decreasing the carbon content of films decreases thetrapping of electrons in the film, and leads to more reliable, longlasting devices.

The deposition rate can be regulated by adjusting the flow rate ofprecursors into the plasma generator and thereby adjusting the flow rateof reactive intermediates over the wafer. However, as the precursor flowrate increases, the residence time within the plasma generatordecreases, and this can result in less complete cracking. To overcomethis problem, it is desirable to increase the plasma power as theprecursor flow rate increases. This maintains the efficiency of thecracking reaction.

If desired, further increases in the efficiency of the plasma reactionscan be achieved by heating the chamber. This can be done using aconventional resistive heater or using an infrared (IR) heater.Preferably, IR irradiation is used, and the wavelength of the IRradiation is chosen to maximal absorption by the precursor.

The above reaction is designed to accommodate wafers with diameters ofabout 200 mm. Thin films of this invention are deposited at a rate ofabout 1000 Å/min. Films deposited using this system have dielectricconstants of 2.3 to 3.5, and have Td in the range of about 350° C. to500° C., depending on the fluorine content. Increasing the fluorinecontent decreases the dielectric constant. The thin films have noinitial weight loss; Td and Tg are temperatures ranging from 450° C. to500° C. under nitrogen atmosphere.

EXAMPLE 2 Manufacture of a Thin Film Low Dielectric Layer Using PlasmaEnhanced Transport Polymerization

A thin film of C₆F₅—Si(OCH₃)₃ is made using a parallel type of plasmareactor as depicted in FIG. 3. The compound is delivered into thechamber employing a bubbling device using Ar as a carrier gas. Thecompound is introduced at a feed rate of 50 SCCM. The operating chamberpressure is 20 milliTorr. Effective plasma is maintained by an RFfrequency of 13.56 MHz at a power of 1.3 Watts/cm² applied to the upperelectrode with a wafer placed on the lower electrode which is grounded.The wafer temperature is maintained at 400° C. The thin film made bythis process has a dielectric constant of 2.65, and has no initialweight loss at 500° C. under nitrogen atmosphere.

C. General Methods for the Manufacture of Low Dielectric Thin FilmsUsing Photon Assisted Transport Polymerization

In addition to thermally and plasma- generated reactive intermediates,photon assisted precursor cracking is also part of this invention.Because specific chemical bonds have specific energies, and becausethese energies can be supplied as photons, electromagnetic radiation isa preferred method of practicing this invention.

A transport polymerization system 400 using electromagnetic radiation isshown in FIG. 4. Precursors are stored in a precursor tank 404 and thenflow through a pipe 408 to a mass flow controller 412, where theprecursor flow rate is regulated. Volatile precursor then passes throughpipe 416 into a transparent tube 420. For UV photolytic cracking of theprecursor, tube 420 is made of quartz, preferably a single quartzcrystal. For infrared (IR) cracking of the precursor, tube 420 may bemade of glass. For vacuum ultraviolet photolytic cracking of theprecursor, tube 420 is made of MgF₂, LiF, or CaF₂. An ultraviolet (UV)source 424 is used to photolytically dissociate the precursor.Alternatively, a vacuum ultraviolet (VUV) 426 source can be used. Aninfrared (IR) source 428 can be used, which heats the precursors toprovide a combination of thermolytic and photolytic cracking. Aftercracking, the intermediates pass into the deposition chamber 432, whichis heated by a resistive heater 436 to prevent deposition ofintermediates on the walls of chamber 432. The flow of intermediates isadjusted using flow pattern adjuster 440. Moving the flow patternadjuster 440 in the vertical direction adjusts the flow rate of and thedistribution pattern of intermediates in the deposition chamber 432.Moving the flow pattern adjuster 440 in the horizontal direction adjuststhe distribution pattern of intermediates in the deposition chamber 432.A gas dispersion plate 444 evens the delivery of the intermediates tothe wafer 448. The wafer 448 is held by a cold chuck 452, which ismaintained at low temperatures by a conventional cooling device, usingliquid nitrogen, reverse Peltier effect, or any other cooling apparatusknown in the art. The chamber 432 is connected via a pipe 460 to a trap464, which is connected via another pipe 468 to a pump 472. The pumpmaintains the pressure within the deposition chamber 432 at the desiredlevel, and the trap 464 minimizes the deposition of intermediates on thepump 472.

Using the photolytic method, the dissociation reaction can be veryselective and efficient if appropriate photon sources are used. Thephoton sources can be provided by ultraviolet (UV) light generated bymercury vapor discharge or metal halide lamps. Exemplary sources of UVradiation for transport polymerization can include (1) a mercury lampthat provides from 50 to 220 mWatts/cm² of UV ranging from 200 to 450 nmor (2) a metal halide lamp that provides from 40 to 160 mWatts/cm² of UVranging from 260 nm to 450 nm. These UV sources provide photon energiesranging from 2 to 5 eV, which are sufficient for generating many radicalintermediates.

An alternative to conventional UV light is vacuum ultraviolet (VUV).Incoherent excimer radiation can provide a large number of UV and VUVwavelengths for photolytic processing of various chemicals. Thepreferred source is incoherent excimer radiation derived from dielectricbarrier discharge. UV and VUV photons that are in the ranges of 3 to 5eV are especially useful. These energy levels are comparable with thebonding energies of most chemical bonds, thus are very effective forinitiating photochemical reactions (see Table 4).

TABLE 4 Bond Energies of Selected Bonds Chemical Bonds Bonding Energies(eV) φ-CH₂Br 2.52 φ-CH₂—OR 3.52 φ-CH₂—CH₃ 3.30 φ-CH₂—NH 3.09 φ-CH₂—F4.17 φ-CH₂—SR 3.20 φ-CH₂—H 3.83

Table 4 shows the bonding energies in electron volts (eV) correspondingto certain bonds of this invention. This data is from Streitwiesser etal., Introduction to Organic Chemistry, Appendix II, University ofCalifornia Press, Berkeley, Calif. (1992), incorporated herein fully byreference.

However, the energies of mercury vapor or metal halide UV radiation aretoo small to be useful for rapid transport polymerization. The desiredresidence time within the cracking chamber, which is the time availablefor photolysis should be in the range of a few milliseconds to severalhundred milliseconds. Therefore, VUV is the most desirable form ofenergy for photon assisted transport polymerization.

VUV or incoherent excimer UV sources can be provided by dielectricbarrier or silent discharge. For example, VUV can be generated usingKrBr, Ar₂, ArCl, ArBr, Xe₂ and F₂ gases. Xe emits at 172 nm, Kr at 222nm, and XeCl emits at 308 nm. As can be seen from Table 2, nearly all ofthe chemical bonds of interest in polymer manufacture can be brokenusing photolytic methods. Because excimer radiation is selective for theenergy of the specific bonds, excimer radiation from another source orplasma may be used simultaneously if it is desired to break other bondsat the same time. Such a combination of excimer and plasma sources areuseful to break bonds of precursors of cross-linkedpoly(para-xylylenes). Because the leaving groups of these precursors maybe different, it is desirable to break those bonds selectively togenerate tri- and tetra-functional reactive intermediates.

When IR incoherent excimer irradiation is used, the conventionalstainless steel or ceramic pipe or reactor used in the pyrolyzer willhave to be replaced with a quartz tube or reactor. When using UV, thetransparent tube shown in FIG. 4 can be made of any UV transparentmaterial such as quartz, preferably a single quartz crystal. When usingVUV, the transparent tube must be made of a material transparent to VUVwavelengths. Crystals of MgF₂, LiF, or CaF₂ are preferred.

TABLE 5 Operating Conditions for Photon Assisted Dissociation ofPrecursors Variable Range Preferred Range Photon Wavelength 100-400 nm140-300 nm Photon Energy 2.5-12 eV 4-9 eV Photon Flux 5 mW/cm²-10 W/cm²40-100 mW/cm² Reaction Chamber Pressure 0.1 milliTorr-10 Torr 1-100milliTorr Reaction Chamber Tem- −20-300° C. 30-100° C. peratureDeposition Chamber Tem- −30 to +20° C. −10° C. perature DepositionChamber Pressure 0.1 milliTorr-10 Torr 1-100 milliTorr

In one embodiment of this invention, photon assisted dissociation occursimmediately above the wafer surface onto which the film is to bedeposited. Because no transport of intermediates is needed, theefficiency of deposition is increased. Further, the photon energy ormixtures of photon energy (from mixed excimer gases) could be made toboth dissociate the precursor as well as promote nucleation and adhesionof the polymer based films.

D. General Methods for the Manufacture of Low Dielectric Thin FilmsUsing Photon-Plasma Assisted Precursor Dissociation and Deposition

Additionally, a combined photon-plasma process is used for dissociationof precursors and deposition of thin films of low dielectric materials.Photon energy is used to generate a plasma in certain gases. In thisembodiment of the invention, the attributes of plasma, generally highrates of dissociation, along with the cool photon energy source,provides a unique method for both precursor dissociation and even filmdeposition. Additionally, infrared (IR) radiation can be used to heatreactor elements and precursors. Pre-heating precursors increases theefficiency of photon and plasma dissociation of the precursors.Moreover, the photon plasma can be directed toward the surface on whichfilms are being deposited.

FIG. 5 depicts a schematic diagram of a TP and CVD reactor 500 embodyingthe elements for photon-plasma and IR dissociation and deposition.Precursors 504 are stored in a precursor container 508 which isconnected via a pipe 512 to a mass flow controller 516. For TP,precursors are transported into a dissociation reactor 524 which housesthe dissociation chamber 528. The wall of reactor 524 is made ofcrystalline materials such as LiF, MgF₂, or CaF₂, which permits light ofvacuum ultraviolet wavelengths to pass. Vacuum ultraviolet andultraviolet light is generated by a silent discharge plasma generators532, which are place inside infrared heaters 536. The infrared heaters536 are placed inside DC magnets 540 and AC magnets 544. The magnetsregulate the flow of plasma during dissociation, and the reactiveintermediates so generated are transported to a deposition reactor 550.

The deposition reactor 550 contains a deposition chamber 560 containinga gas and reactant dispersion manifold 554, a gas and reactantdispersion plate 558. The walls of the deposition chamber are made ofcrystalline materials such as LiF, MgF₂, or CaF₂, which permits light ofvacuum ultraviolet wavelengths to pass. The gas dispersion manifold 554and the gas dispersion plate 558, are used to adjust the distributionand homogeneity of the intermediates. The intermediates are directedtoward the wafer 562, which is held on a cold chuck 564. The gasdispersion manifold 554 and dispersion plate 558 are connected inparallel to a DC voltage bias anode 568, a DC voltage bias cathode 569,an AC voltage bias anode 570, and an AC voltage bias cathode 571. Silentdischarge plasma generators 572 are placed outside the depositionchamber 560. Infrared heaters 574 are placed outside the silent plasmadischarge generators 560 and DC magnets 578 and AC magnets 580 areplaced outside the infrared heaters 574. Gases exit the depositionchamber 560 through a pipe 584, pass through a cold or reactive trap588, pass through another pipe 592 to a vacuum pump 596. The pressure inthe systems is maintained at a desired pressure using pump 596. The trap588 protects the pump from deposition of intermediates.

For CVD, the deposition chamber can be used without the dissociationreactor.

Precursors are placed directly on wafer 562, and the chuck 564 is notcooled. IR, UV, or VUV radiation is directed toward the wafer 562. Theradiation dissociates the precursor, and deposition of intermediates andpolymerization takes place on the wafer.

Table 6 shows process conditions for combined photon-plasma assistedprecursor dissociation using chamber 528, and Table 7 shows processconditions for combined photon-plasma precursor deposition in chamber560.

TABLE 6 Process Conditions for Photon-Plasma Precursor DissociationVariable Range Preferred Range Temperature 200° C.-600° C. 350° C.-500°C. Photon Wavelength 100 nm-400 nm 140 nm-300 nm Photon Energy 2.5 eV-12eV 4 eV-9 eV Photon Flux 10 milliW/cm²-5 W/cm² 40-100 milliW/cm² PlasmaDensity 10¹²-10¹⁴ electrons/cm³ 10¹³ electrons/cm³ Pressure 0.1milliTorr-10 Torr 1 milliTorr-10 milliTorr

TABLE 7 Process Conditions for Photon-Plasma Precursor DepositionVariable Range Preferred Range Temperature −20° C.-300° C. −10° C.Photon Wavelength 100 nm-400 nm 250 nm Photon Energy 2.5 eV-12 eV 4.5 eVPhoton Flux 10 milliW/cm²-5 W/cm² 10-100 milliW/cm² Plasma Density10¹²-10¹⁴ electrons/cm³ 10¹³ electrons/cm³ Pressure 0.1 milliTorr-10Torr 1 milliTorr-10 milliTorr

In Tables 6 and 7, the plasma density is reported as electron density,but it is to be noted that ion density must be the same to maintaincharge neutrality of the plasma. Any non-uniformity of chargedistribution can result in plasma damage to the thin film of lowdielectric material, as well as imparting charge to the integratedcircuit components.

Control of the plasma is by a magnetic field within the precursorchamber and in the deposition chamber. In the precursor reactor, theplasma is confined to any desired area, such as the center of thereactor. Additionally, by alternating the polarity of the magnetic fieldstirs the plasma, ensuring even energy distribution within the plasma,thereby increasing the efficiency of dissociation of precursor moleculesinto reactive intermediates. In the deposition chamber, the magneticfield is used to control the pattern of distribution of intermediatesover the wafer. This would serve two purposes: (1) to direct thedeposition of precursor to the desired portion of the surface, thusconserving the precursor, and (2) minimize film deposition on otherparts of the reactor chamber, thus minimizing the required cleaning,minimizing particle generation, and simplifying the reactor chamberdesign.

Another feature comprises the placement of an electrical bias voltagewithin the deposition chamber. This provides a further means ofcontrolling the flow of plasma-ionized species to the site of depositionon the wafer. A bias voltage, in the form of direct current (DC) oralternating current (AC) can be applied and modulated. Pulsed voltagescan be used to alter the flow pattern of ions to either accelerate,decelerate, or to regulate the density of the plasma ions in the streamreaching the wafer. Optimization of ion velocity and flow, thus can beobtained using various combinations of magnetic field and bias voltage.

TABLE 8 Optimization of Electrical and Magnetic Field Variables VariableRange Preferred Range DC Bias Voltage 100-2000 V 500 V AC Bias Voltage10-200 V 50 V Pulsed Bias Voltage 100-4000 V 500 V Pulse Width 10-1000msec 1 msec Pulse Frequency 10 Hz-1000 Hz 60 Hz DC Magnetic FieldStrength 100-2000 Gauss 700 Gauss AC Magnetic Field Strength 100-1000Gauss 500 Gauss AC frequency 10 Hz-500 Hz 50 Hz-60 Hz

Table 8 shows the ranges of the various magnetic field and bias voltagevariables which are regulated in this invention.

Other reactors and reactor configurations may be used, as exemplified bythe above cited co-pending applications incorporated herein fully byreference.

The low dielectric constant materials are polymerized into thin films ofthicknesses of about 500 Å to about 5 μm on wafers for use in themanufacture of integrated circuits. FIG. 6 depicts a diagram of amultilevel integrated circuit chip 600 embodying the features of thisinvention. The substrate 604 has a source region 608, a drain region612, and a polysilicon gate 616. A first interlevel dielectric (ILD)layer 620 overlays the substrate 600 and polysilicate gate 616. Thewafer is subsequently planarized using chemical mechanical polishinganother method known in the art. A floating polysilicon gate 624 isoverlain by a second ILD layer 628. the wafer is again planarized, afirst metal line 632 and a first intermetal dielectric (IMD) layer 636are deposited. The wafer is again polished. On top of the IMD layer 636,a third metal line 640 and a second ILD layer 644 is deposited. Thewafer is again planarized.

It should be appreciated by those of ordinary skill in the art thatother embodiments may incorporate the concepts, methods, precursors,polymers, films, and devices of the above description and examples. Thedescription and examples contained herein are not intended to limit thescope of the invention, but are included for illustration purposes only.It is to be understood that other embodiments of the invention can bedeveloped and fall within the spirit and scope of the invention andclaims.

Other features, aspects and objects of the invention can be obtainedfrom a review of the figures and the claims.

INDUSTRIAL APPLICABILITY

The invention includes novel precursors containing a fluorinated silane,fluorinated siloxane and fluorocarbons, each containing a fluorinatedaromatic moiety. The precursors are suitable for making polymers withlow dielectric constants and high thermal stability.

Additionally, the invention includes methods for making polymers forintegrated circuit manufacture using novel fluorinated siloxanes,fluorocarbons, and fluorinated aromatic moieties.

Furthermore, the invention includes integrated circuits made usingfluorinated siloxanes, fluorocarbons, or fluorinated aromatic moieties,with low dielectric constants.

According to the present invention, the polymers made from the disclosedprecursors have low dielectric constant and high thermal stability.Therefore, integrated circuits made from these precursors have improvedelectrical and mechanical properties.

What is claimed is:
 1. A precursor for making a low dielectric constantmaterial, the precursor comprising a fluorinated moiety with at leastone of a sp²C—F bond and hyperconjugated sp³C—F bond, said precursorselected from the group consisting of (1) a fluorinated silane, (2) afluorinated siloxane and (3) a fluorocarbon having only a singlearomatic moiety.
 2. The precursor of claim 1 comprising(C₆H_(5-n)F_(n))_(m)—SiH_(4-m) wherein m is an integer selected from thegroup of 1, 2 and 3 and wherein n is an integer selected from the groupof 1, 2, 3, 4 and
 5. 3. The precursor of claim 1 comprising(C₆H_(5-n)F_(n))_(m)—Si(OCH₃)_(4-m) wherein m is an integer selectedfrom the group of 1, 2 and 3, and wherein n is an integer selected fromthe group of 1, 2, 3, 4 and
 5. 4. The precursor of claim 1 comprisingC₆F₅—CF₃.
 5. The precursor of claim 1 comprising C₆F₅—CHF₂.
 6. Theprecursor of claim 1 comprising C₆F₅—CH₂F.
 7. The precursor of claim 1comprising C₆F₅—CH₃.
 8. The precursor of claim 1 comprising C₆F₅—CF═CF₂.9. The precursor of claim 1 comprising(CH_(3-n)F_(n))—(C₆H_(4- p)F_(p))—(CH_(3-m)F_(m)) wherein n and m areintegers selected from the group consisting of 1, 2 and 3, and p is aninteger selected from the group consisting of 1, 2, 3, and
 4. 10. Theprecursor of claim 1 comprising HCF₂—C₆F₄—CF₂H.
 11. The precursor ofclaim 1 comprising CH₂F—C₆F₄—CH₂F.
 12. The precursor of claim 1comprising CF₃—C₆F₄—CF₃.
 13. The precursor of claim 1 comprisingCH₃—C₆F₄—CH₃.
 14. The precursor according to claim 1 wherein saidprecursor contains no C—H bonds.
 15. The precursor of claim 1 whereinthe fluorinated moiety is an aromatic moiety.
 16. The precursor of claim1, wherein the precursor comprises a mixture of a fluorocarbon and afluorinated siloxane.
 17. The precursor of claim 2 comprising C₆F₅—SiH₃.18. The precursor of claim 2 comprising (C₆F₅)₂—SiH₂.
 19. The precursorof claim 3 comprising C₆F₅—Si(OCH₃)₃.
 20. The precursor of claim 3comprising (C₆F₅)₂—Si(OCH₃)₂.
 21. The precursor of claim 1 comprising(C₆F₅)_(n)—CHF_(3-n), wherein n is an integer selected from the groupconsisting of 1, and
 2. 22. The precursor of claim 1 comprising(C₆H_(5-n)F_(n))_(m)—SiH_(4—m) wherein n in an integer selected from thegroup consisting of 1, 2, 3, 4, and 5, and wherein m is an integerselected from the group of 1, 2 and
 3. 23. The precursor of claim 1comprising (C₆H_(5-n)F_(n))_(m)—Si(OCH₃)_(4-m) wherein m in an integerselected from the group consisting of 1, 2, 3, 4, and 5, and wherein mis an integer selected from the group of 1, 2, and
 3. 24. The precursorof claim 1 comprising (C₆H_(5-n)F_(n))—CH_(1-m)F_(m)═CH_(2- p)F_(p),wherein n is an integer selected from the group consisting of 1, 2, 3, 4and 5, wherein m is a integer selected from the group consisting of 0and 1, and wherein p is an integer selected from the group consisting of0, 1 and 2.